Heat actuated contact unit for electrical fire alarm systems

ABSTRACT

A totally sealed twin chamber thermostat for an electrical fire alarm system actuated by both slow and fast heat rise conditions.

United States Patent Inventor Paul Henry Ripamonti Baulkhnm Hills, New South Wales, Australia App]. No. 752,650 Filed Aug. 14, 1968 Patented Mar. 9, 1971 Assignee Fire Fighting Equipment Pty., Limited Ermington, New South Wales, Australia Priority Nov. 16, 1967 Australia 29,962/67 HEAT ACTUATED CONTACT UNIT FOR ELECTRICAL FIRE ALARM SYSTEMS Primary Examiner-G. Harris Assistant Examiner-Dewitt M. Morgan Attorney-Naylor & Neal ABSTRACT: A totally sealed twin chamber thermostat for an electrical fire alarm system actuated by both slow and fast heat rise conditions.

7 Claims, 4 Drawing Figs.

U. S. Cl. 337/320, 337/407 Int. Cl. H01h 37/40, H01h 37/76 HEAT ACTUATED CONTACT UNIT FOR ELECTRICAL FIRE ALARM SYSTEMS This invention relates to heat actuated contact units used in buildings to operate electrical fire alarm systems when subjected to a determined elevated temperature.

The invention has been devised to provide a heat actuated contact unit which can be factory set and hermetically sealed thereby eliminating such corrosive action as may be due to atmospheric conditions.

This heat actuated contact unit comprises a base, terminals on the base for connecting the contact unit into a fire alarm circuit, a first airtight chamber, a diaphragm forming a wall of the first chamber, two contacts in the first chamber respectively connected to the terminals, one of said contacts being electrically connectable to the other of said contacts by the deflection of the diaphragm; a cap made of material having heat transfer properties mounted on the base over the first chamber to form a second airtight chamber with said diaphragm forming a partition between the chambers, a pusher in the second chamber adapted to deflect the diaphragm, said pusher being held inoperative by a low melting solder.

Two embodiments of the invention are described with reference to the accompanying drawings in which:

FIG. 1 is an exploded perspective view of the contact unit,

FIG. 2 is a sectional elevation of the contact unit assembly,

FIG. 3 is a view similar to FIG. 2 showing how the electric circuit is complete from the unit, and

' FIG. 4 is a view similar to FIG. 2 showing an alternative construction.

Referring to the drawings 1 to 3; the base 1 is made of dielectric material and has a circular well 2 formed therein. A ring 3 integral with the base 1 is set upwardly from the bottom 4 of the well to form a shallow annular space 5 between the ring 3 and the wall of the well. The base has holes 6 to take mounting screws. Two terminals 7 and 8 are mounted on the bottom of the base 1 by screws 9 and 10 which project through the base 1 into the well. Electric contacts 11 and 12 are secured to the bottom 4 of the well inside the ring 3 by the screws 9 and 10. Contact 11 projects upwardly from the bottom 4 and extends part way across the top of the ring 3 while contact 12 projects upwardly from the bottom 4 approximately in the center of the well.

A metallic sleeve 13 having an outside diameter less than the diameter of the well and an internal diameter slightly greater than the outside diameter of the ring 3 has an internal abutment ring 14 and a metallic diaphragm 15 is soldered into a locating step 16 formed by the abutment ring 14 and the sleeve 13. There is a bleed hole 17 through the diaphragm l5 sealed with a low melting solder. The sleeve 13 is mounted in the annular space 5 with the abutment ring 14 seating on top .of the ring 3. The sleeve 13 and the abutment ring 14 are secured to the ring 3 with a suitable adhesive thereby forming a first sealed chamber A. In this position the contact 11 makes contact with the abutment ring 14 while the contact 12 is spaced slightly from the underface of the diaphragm 15.

A cap 18 made from heat conductive material, which as illustrated is of a generally domed shape, has a cylindrical part 19 which is dimensioned to fit between the wall of the well and the outer face of the sleeve 13, and is secured in place by a suitable adhesive so as to form a second sealed chamber B with the diaphragm 15 forming a partition between the two chambers. A metallic diaphragm pusher 20 has a long limb 21 and a short limb 22 both of which are flanged at their free ends as at 23 and 24 respectively. The flange 23 is fixed to the inner wall of the cap 18 by a heat resisting solder and the flange 24 is secured to the inner wall of the cap by a low melting solder. The diaphragm pusher 20 is dimensioned, located and biassed so that on release of the flange 24 the limb 22 at the point of connection to the limb 21 will engage the diaphragm 15 and force it against the contact 12 as illustrated in HG. 3.

It will be understood that the sleeve and diaphragm may be made from any suitable material provided a conductive path between the terminals results from engagement between the diaphragm l5 and the contact l2.

A fast rise in ambient temperature heats and expands the air in the chamber B before the heat can reach the chamber A. When the pressure of air in chamber B reaches a predetermined pressure, the diaphragm 15 is moved thereby and completes the electric circuit by pressing against contact 12. This could happen prior to the release of the diaphragm pusher 20.

A slow rise in ambient temperature will heat and expand the air in both chambers A and B so that the diaphragm 15 may be held in equilibrium. When predetermined temperature is reached the solder in bleed hole 17 and the solder securing the flange 24 to cap 18 melts, thereby releasing the pusher which moves the diaphragm 15 to complete the electric circuit. The opening of the bleed hole 17 allows the pressure in the chambers A and B to equalize when the diaphragm is deflected.

It is also within the scope of the invention to provide a pressure operated valve member over the bleed hole 17 so that continual equalization of the air pressure in chambers A and B is achieved.

As hereinbefore described the conductive path from one terminal to the other is through a metallic diaphragm. It'is within the scope of the invention to provide contact connecting means operable by the deflection of the diaphragm (see FIG. 4). Such means may be in the form of a spring arm extension 25 of contact 11, the arm 25 is adapted to connect contact 11 to contact 12 as the arm 25 is deflected by the diaphragm 15.

It will be understood that an inert gas may be used to charge the chambers. The cubic capacity of one chamber may be proportioned, relative to the other to achieve a determined operation of the unit under fast temperature rise conditions.

lclaim:

l. A heat actuated contact unit for electrical fire alarm systems, said unit comprising a base, terminals on the base for connecting the contact unit into a fire alarm circuit, a first airtight chamber formed by said base member and a diaphragm forming a wall of the first chamber, two contacts in the first chamber respectively connected to the terminals, one of said contacts being electrically connectable to the other of said contacts in response to deflection of the diaphragm; a cap made of material having heat transfer properties mounted on the base over the first chamber to form a second airtight chamber with said diaphragm forming a partition between the chambers, whereby a fast rise in ambient temperature will expand the air in said second chamber to deflect said diaphragm, and a pusher mounted in the second chamber for movement relative to the diaphragm to deflect the diaphragm, said pusher being held in an operative condition against movement relative to the diaphragm by a low melting solder, said solder adapted to melt in response to a slow rise in ambient temperature, thereby releasing said pusher so that it deflects said diaphragm.

2. The contact unit claimed in claim 1 wherein saId base is made of dielectric material, said first airtight chamber being further formed by a metallic sleeve fixed at one end to said base and projecting upwardly from the base, said diaphragm being made of metal and fixed over the other end of said sleeve, said second chamber being defined by a generally domed metallic cap fixed at its open end to the base.

3. The contact unit claimed in claim 2 wherein said base is provided with a well having a ring integral with the base extending upwardly from the bottom of the well and said sleeve is fixed to said ring, the open end of said cap lying between the sleeve and the wall of the well.

4. The contact unit claimed in claim 3 wherein the sleeve has an internal abutment ring adapted to seat on the end of the ring integral with the base.

5. The contact unit claimed in claim 4 wherein said one contact is electrically connected to said sleeve.

6. The contact unit claimed in claim 1 wherein said diaphragm has a bleed hole therethrough sealed with low melting solder.

7 The contact unit claimed in claim 1 wherein diaphragm has a bleed hole therethrough adapted to provide selective communication between said chambers. 

1. A heat actuated contact unit for electrical fire alarm systems, said unit comprising a base, terminals on the base for connecting the contact unit into a fire alarm circuit, a first airtight chamber formed by said base member and a diaphragm forming a wall of the first chamber, two contacts in the first chamber respectively connected to the terminals, one of said contacts being electrically connectable to the other of said contacts in response to deflection of the diaphragm; a cap made of material haVing heat transfer properties mounted on the base over the first chamber to form a second airtight chamber with said diaphragm forming a partition between the chambers, whereby a fast rise in ambient temperature will expand the air in said second chamber to deflect said diaphragm, and a pusher mounted in the second chamber for movement relative to the diaphragm to deflect the diaphragm, said pusher being held in an operative condition against movement relative to the diaphragm by a low melting solder, said solder adapted to melt in response to a slow rise in ambient temperature, thereby releasing said pusher so that it deflects said diaphragm.
 2. The contact unit claimed in claim 1 wherein saId base is made of dielectric mateRial, said first airtight chamber being further formed by a metallic sleeve fixed at one end to said base and projecting upwardly from the base, said diaphragm being made of metal and fixed over the other end of said sleeve, said second chamber being defined by a generally domed metallic cap fixed at its open end to the base.
 3. The contact unit claimed in claim 2 wherein said base is provided with a well having a ring integral with the base extending upwardly from the bottom of the well and said sleeve is fixed to said ring, the open end of said cap lying between the sleeve and the wall of the well.
 4. The contact unit claimed in claim 3 wherein the sleeve has an internal abutment ring adapted to seat on the end of the ring integral with the base.
 5. The contact unit claimed in claim 4 wherein said one contact is electrically connected to said sleeve.
 6. The contact unit claimed in claim 1 wherein said diaphragm has a bleed hole therethrough sealed with low melting solder.
 7. The contact unit claimed in claim 1 wherein said diaphragm has a bleed hole therethrough adapted to provide selective communication between said chambers. 